1. Field of the Invention
The present invention relates to a method of forming a silicon deposition film and, more particularly, to a method of forming a deposition film of amorphous silicon (to be referred to as an a-Si) or polycrystalline silicon (to be referred to as a poly-Si hereinafter) which is suitably used as a photoconductive film, a semiconductor film or an insulating film.
2. Description of the Prior Art
It is conventionally known that SiH.sub.4 or Si.sub.2 H.sub.6 is used as a material to deposit an a-Si film by a glow discharge or thermal energy deposition technique. More particularly, SiH.sub.4 or Si.sub.2 H.sub.6 is excited and decomposed by electrical or thermal energy to deposit the a-Si film on a substrate. The a-Si film is used in a variety of applications.
However, when SiH.sub.4 or Si.sub.2 H.sub.6 is used as a material in glow discharge deposition, the influence of high power discharge energy on a deposition film is excessively large and frequently precludes control of stable deposition conditions with good reproducibility. In particular, when a thick film of large area is deposited on a substrate, the above tendency becomes predominant.
In conventional thermal energy deposition, a high temperature is required to limit the type of usable substrate. in addition, effective hydrogen atoms bonded in a-Si are dissociated therefrom at a higher rate. As a result, desired properties of the deposition film cannot be obtained.
As is apparent from the above description, since the deposition film is formed using SiH.sub.4 or Si.sub.2 H.sub.6, the electrical and light characteristics thereof are not uniform, and film quality is poor. Crystal defects in the surface layer of the deposition film and defects within the bulk tend to occur. These problems must be resolved.
In order to resolve the above problems, a light energy deposition technique (i.e., a photo-CVD method) using SiH.sub.4 and Si.sub.2 H.sub.6 as a starting material has been recently proposed and is receiving a great deal of attention. This technique has an advantage in that an a-Si deposition film can be fomred at a low temperature, thereby greatly alleviating the conventional problems. However, since light energy has a relatively low excitation level, effective decomposition of SiH.sub.4 or Si.sub.2 H.sub.6 cannot be realized so that deposition rate is kept low and mass production cannot be effectively performed.